A range of hydrocarbon-based fuel compositions have been developed over the years for use in operating a wide range of internal combustion engines. Such fuels include both gasoline, used as the primary fuel for automotive vehicles, and diesel, used as the fuel for a wide range of trucks, trains, ships, and other automotive applications. For many years, the fuel compositions, while effective for providing the necessary power from the engines in which they were employed, suffered the disadvantage of producing a range of exhaust products that are both hazardous and environmentally unfriendly. In recent years, however, problems associated with the products from combusting hydrocarbon-containing fuels have been recognized and there has been a growing need for improved hydrocarbon-based fuel compositions, which meet the needs of the engines in which they are employed while producing an exhaust product which is less detrimental to the environment.
For example, gasoline was for many years blended with lead-containing compounds, most typically tetraethyl lead, in order to provide the fuel with the necessary octane rating and provide lubrication for certain components of gasoline-powered internal combustion engines. Following the recognition of the harmful effects on the environment of the lead-containing products present in the exhaust gases of engines burning lead-containing fuels, a range of unleaded gasoline compositions were developed and made available. Further, diesel fuel compositions have products of combustion having high concentrations of carbon, carbon monoxide and various oxides of nitrogen when combusted in an internal combustion engine.
With the significant recent interest in producing clean hydrocarbon fuels for automotive vehicles and the like, there has been a growing need for improved hydrocarbon fuels which do not give rise to the aforementioned exhaust gas and emissions problems.
German Patent Publication No. 25 23 992 discloses a fuel composition for automotive vehicles. The fuel composition is a lead-free composition, which is alleged to result in a reduction in the production of environmentally harmful components. The fuel composition disclosed in DE 25 23 992 comprises from 10 to 75% gasoline or a gasoline component; from 15 to 40% of methanol, ethanol or a mixture of the same; from 2 to 15% of an ester of acetic acid with an alcohol having from 1 to 6 carbon atoms; and, either in addition to the aforementioned components or in place of the ester of acetic acid, from 4 to 20% higher alcohols. Examples 1 and 2 of DE 25 35 992 are directed to fuel compositions comprising gasoline and reformate as the base hydrocarbon respectively. In both compositions, a major portion of the remaining components is made up of one or more alcohols, in particular methanol and higher alcohols. In the formulations of both Examples 1 and 2, ethyl acetate is present in a minor quantity of 7.2 and 6.8% volume respectively. Example 3 of DE 25 35 992 is directed to a fuel composition consisting of gasoline and alcohols. Example 4 combines gasoline with 22.5% volume methanol and higher alcohols and 2.5 volume % ethyl acetate. It will be noted that all the compositions disclosed in DE 25 35 992 either contain an ester of acetic acid in only a minor amount in combination with a major portion of methanol or higher alcohols, or employ alcohols alone in the absence of an ester.
U.S. Pat. No. 4,806,129 discloses a fuel extender for use with a lead-free gasoline. The extender comprises naphtha as the principal hydrocarbon component, in combination with ethanol and a range of aromatic hydrocarbons, in particular benzene, toluene and xylene. The extender further comprises a stabilizer and a water repellent. The extender is added to lead-free gasoline in an amount of up to 35% volume. Ethanol is present in the extender in a range of amounts of from 3.8 to 6.0% volume. In addition, U.S. Pat. No. 4,806,129 teaches to include isopropyl alcohol in the extender in an amount of from 1.8 to 2.4% volume. As water repellants, U.S. Pat. No. 4,806,129 discloses using either ethyl acetate or methyl isobutyl ketone (MIBK). Each of ethyl acetate and methyl isobutyl ketone may be present in an amount of from 0.2 to 5.75% volume, or more optimally from 0.2 to 3.5% volume, of the extender composition. This equates to the water repellent component being present in the final fuel blend in an amount of up to 2.01% volume. However, the disclosure of U.S. Pat. No. 4,806,129 limits the total content of the water repellent components to be just 4.8 to 20% by volume of the total ethanol content. Thus, the fuel extender and blended fuel compositions of U.S. Pat. No. 4,806,129 comprise ethanol and isopropyl alcohol as the major oxygen-containing component, in combination with a minor stabilizing amount of one or both of ethyl acetate and methyl isobutyl ketone. It is noted that U.S. Pat. No. 4,806,129 indicates a preference for methyl isobutyl ketone as the stabilizing component, due to its higher effectiveness in comparison to ethyl acetate.
European Patent No. 0 708 808 discloses a fuel blend composition, in particular a blend comprising diesel as the base hydrocarbon fuel component. EP 0 708 808 addresses the problem of pollutants being present in the exhaust gases of internal combustion engines operated on conventional diesel blends. EP 0 708 808 notes that a blend containing diesel and up to 15% by volume of ethanol or methanol is been found to improve the quality of exhaust gas emissions, without requiring modifications to existing diesel engine configurations. However, it is also noted that alcohols, such as methanol and ethanol are immiscible with diesel oil, leading to problems with the formulation and storage of the diesel/alcohol fuel blends. As a solution, EP 0 708 808 proposes a fuel blend comprising diesel oil or gasoil, up to 20% by volume of a light alcohol selected from ethanol, n-propanol and mixtures thereof, and up to 15% by volume of a coupling agent. The coupling agent comprises an organic ester. A range of organic esters suitable for use as the coupling agent are disclosed, including fatty esters such as ethyl oleate, ethyl tallowate, iso-propyl oleate, butyl oleate, methyl oleate or methyl cocoate and/or other aromatic esters such as butyl benzoate and/or other aliphatic esters such as methyl acetate or mixtures thereof and/or dicarboxylic acid esters such as dioctyl maleate. A wide range of fuel compositions and fuel additive compositions are exemplified in EP 0 708 808 containing a range of the aforementioned esters. In all the exemplified fuel and additive compositions, the ester is present in only a minor amount in comparison with the alcohol, seemingly in sufficient amount to provide the necessary coupling action and ensure miscibility of the alcohol with the diesel or gasoil fuel.
Current regulations specify that gasoline sold in certain regions of the United States of America that are experiencing high pollution levels and poor air quality should be oxygenated to an oxygen content of 2.7% by weight. Similar proposals are currently being proposed for future regulations regarding the oxygen-containing level of diesel fuel, with a figure of 7% by weight oxygen-content for diesel fuels currently being considered.
Accordingly, it will be appreciated that there is a need for a fuel composition to meet the current and proposed future requirements of the regulations regarding fuel content and emissions levels.
“U.S. Clean Air Act expands role for oxygenates”, G.H. Unzelman, Oil & Gas Journal, Apr. 15, 1991, discusses the issue of oxygenates in fuels, in particular gasoline. A wide range of oxygen-containing compounds for possible inclusion in gasoline blends are mentioned, including alcohols, ethers and esters. It is stated that the oxygenates most likely to be suitable candidates for use in gasoline are ethers, such as methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE) and tertiary amyl methyl ether (TAME), and alcohols, such as methanol, ethanol and tertiary butyl alcohol (TBA). Esters are mentioned as possible oxygen-containing compounds for use in gasoline. Methyl acetate, ethyl acetate and isopropyl acetate are specifically mentioned. However, their proposed use is limited to gasoline blending components to be used in conjunction with methanol as the oxygen-providing component of the gasoline.